In general, aluminum is widely used in a variety of industrial fields because aluminum is lightweight, easily cast, easily alloyed with other metals, easily machined at room temperature and high temperature, and has good electrical and thermal conductivity. Especially, aluminum alloys formed by mixing aluminum with other metals have recently become popular in cars and electronic goods, for the purpose of high fuel efficiency or weight reduction.
Typically, a product is fabricated of an aluminum alloy by forming a case through press molding and forming an anodic oxide film on the surface of the case. According to this method, the case has a surface durable over a long term and a sophisticated color, but its design is limited because there are shapes not available by press molding.
Accordingly, die casting is widely used to fabricate a product of an aluminum alloy. Die casting is a fine casting process in which a die cast identical to a mold machined precisely into the shape of a required cast is achieved by forcing a molten metal into the mold. Since products fabricated by die casting have precise dimensions, need no finishing, exhibit excellent mechanical properties, allow mass production, and require low production cost, die casting is most popular with high mass productivity, in various fields including vehicle parts, electrical devices, optical devices, and meters.
At present, Al—Si series of alloys including ALDC3, ALDC10, and ALDC12, and Al—Mg series of alloys including ALDC5 or ALDC6, which have high die castability, are used widely as aluminum alloys for die casting. However, because these die-casting aluminum materials exhibit poor corrosion resistance, they have limitations in their use in a wide range of applications. Although the poor corrosion resistance may be improved by forming a protection film on the surface of an alloy by physical deposition using an expensive vacuum equipment, a shortcoming of this method is that an additional expensive equipment is required and may not be reused. An ion injection technique of injecting ions of a corrosion-resistant element into the surface of an alloy, and a laser annealing technique of rendering a surface layer to be in a quasi-stable state by projecting a laser beam onto the surface of an alloy are also available. However, the former has a limit on an ion injection depth, and thus if an ion injection layer is damaged during use, corrosion resistance is rapidly decreased. In the latter, the size of a product is changed during processing, which requires additional machine processing.
Accordingly, there is a need for developing a new aluminum alloy for die casting, which is lightweight and durable, facilitates molding of products in various shapes, and has more excellent corrosion resistance than a conventional aluminum alloy even without post-processing of the surface of a product.
In this context, the present inventor completed the present invention by discovering an alloy composition and an optimal composition ratio which can improve corrosion resistance and significantly reduce the weight of a molded product without the need for additional surface processing such as conventional anodizing, compared to a conventional die-casting aluminum alloy, as a result of making efforts to develop a method for reducing the weight of an aluminum alloy and improving the corrosion resistance of the aluminum alloy, while maintaining the properties of the aluminum alloy in view of the characteristics of each component, by mixing pure aluminum with various alloy elements such as Si, Fe, Cu, Mn, Mg, Cr, Ni, Zn, Ti, Pb, Be, Co, and Sn in predetermined amounts.